1. Field of the Invention
The present invention relates to an image coding method, an image coding device, an image processing apparatus, and an image transmitting/receiving system and, more particularly, to a process for encoding image data with consideration given to a delay in transmission of encoded image data.
2. Description of the Related Art
It is common to transmit data representing a moving image or a still image (hereinafter, collectively referred to as “image”) captured using a security camera, a vehicle-mounted camera, or the like to an image receiving apparatus over a network. The amount of data transmitted in this manner increases in proportion to image quality such as resolution, frame rate, and bit depth. However, because the bandwidth of a network for use in such transmission image data is limited, a restriction is imposed on quality of image data to be transmitted.
To enable transmission of image data of higher quality with such a limited network bandwidth, it is general compress image data using a codec such as a JPEG (joint photographic experts group) codec or an H.264 codec and transmit the compressed image data.
It is proposed to packetize image data, which is transformed by line-based wavelet transformation and is it units of a precinct, by rearrangement for each frequency component for the purpose of transmitting the image data with low delay and efficiently, (see, for example, Japanese Laid-open Patent Application No. 2008-028511).
An image compression process is typically performed in units of a fixed data amount. For example, a JPEG compression process is performed by accumulating image data in buffers or the like until the image data of at least 8 lines is stored, and performing the compression process in units of accumulated image data of 8 lines. When the compression process is performed in units of a determined number of lines in this manner, the compression process waits for the image data of the necessary number of lines to be buffered, which can cause a delay in transmission of compressed image data and impair real-time transmission. A similar problem arises as well in the technique disclosed in Japanese Laid-open Patent Application No. 2008-028541 because this technique includes suspending line-based wavelet transformation until a necessary number of lines are buffered.
Under the circumstances, there is a need for a technique for reducing a transmission delay caused by image data compression.